Conventional heavy-duty vehicle air brake systems typically use mechanical pneumatic push-pull control valves to control a vehicle's parking brakes. These large, pneumatic push-pull valves are usually placed within the vehicle's instrument panel, as are the pneumatic lines and connectors used to connect the brake control valves to the other components of the vehicle's air brake system. Dash mounting of these components may decrease pneumatic performance while consuming critical space in the vehicle's instrument panel which may ultimately result in dash configurations that are detrimental to the driver's comfort and convenience. Furthermore, installation of the pneumatic instrument panel controls requires complex, airtight connections during the final assembly phase of the vehicle. Thus, there is a need for a system that removes the pneumatic lines from a vehicle's dashboard while maintaining the basic functions and overall characteristics of currently used brake systems.
Some prior art braking systems have utilized electric controls to address the problem of limited dashboard space. Such systems typically include an electrical switch assembly mounted on or in the instrument panel for controlling the parking brakes with an electrically responsive valve located remotely from the dash components. One problematic aspect of these systems is that when electrical power is lost to the valve, the valve moves to its exhaust position, drops the parking brake line pressure to atmospheric pressure, and applies the vehicle's parking brake. Loss of electrical power or connectivity to a vehicle's brake system may be the result of loose terminal connections, broken wires, a dead battery, or other unforeseen events. As will be appreciated by those skilled in the art, inadvertent engagement of the parking brake may create an extremely dangerous situation if the vehicle is moving at any appreciable speed. Thus, there is a need for an air brake system that includes the use of electronics, but that prevents the inadvertent application of the vehicle's parking brakes should power to the brake control system be lost.